The present application relates to integrated circuit motor controllers.
In a typical closed loop control system (e.g. motor speed control), a means of introducing phase lead/lag is common to ensure loop stability. FIG. 1 is a simplified block diagram of the motor speed control loop found in an example of a spindle motor controller. Although not shown, an electronic circuit compares the motor speed and phase to a precision reference and generates a command voltage that controls the amount of current flowing in the motor. The speed is therefore controlled by controlling the motor current.
In order to compensate for the pole of the motor, a filter amplifier is normally used to shift the phase. In its simplest form, a resistor and capacitor form an integrator. The drawback of this scheme is that a finite time is required for the loop to settle when the motor is first spun up. In the prior art this time was greater than 10 seconds, which is excessively long for a system that must quickly spin up a hard disk drive for a computer system.
This excessive settling time is caused by the large output swing capability of the filter amplifier itself. The large output voltage swing requires that the capacitor be charged/discharged to the full range of the output voltage before it eventually settles to the normal operating point. This large swing is required to allow the controller to work with a variety of motors that have different requirements for start up current. Normally the start up current is roughly 10 times higher than the running current.
The present invention provides an improved motor control circuit, including an improved filter amplifier which includes a clamping circuit to limit the maximum voltage of the filter amplifier. The clamping circuit is controlled by a clamping voltage which is normally present anyway (since this voltage is used to limit the amount of maximum current in the motor). Since this level of current is selected to ensure adequate current during start up, this signal is therefore appropriate to limit the output voltage of the filter amplifier. With this improvement (which adds very little circuit complexity), the settling time has been reduced to under 4 seconds. Further optimization of the embedding network can provide further improvement in settling time.
According to a disclosed class of innovative embodiments, there is provided: a control circuit, comprising: a filter amplifier comprising a first input operatively connected to receive a command voltage and a second input operatively connected to receive a reference voltage, and further comprising one or more passive elements connected therewith; an error amplifier, integrated with said filter amplifier, and comprising a first input operatively connected to be driven by an output of said filter amplifier, an output connectable to drive a power transistor, and a second input connectable to receive a feedback value which is proportional to the current passed by the power transistor; wherein said filter amplifier and said error amplifier each comprise: a respective output transistor of a first majority-carrier conduction type connected to drive said respective output, and a respective clamp transistor of a second majority-carrier conduction type connected to limit the voltage on a control terminal of said respective output transistor, both said clamp transistors having respective control terminals thereof connected to a common constant voltage.
According to another disclosed class of innovative embodiments, there is provided: a control circuit, comprising: a filter amplifier comprising a first input operatively connected to receive a command voltage and a second input operatively connected to receive a reference voltage, and further comprising one or more passive elements connected therewith; an error amplifier, integrated with said filter amplifier, and comprising a first input operatively connected to be driven by an output of said filter amplifier, an output connectable to drive a power transistor, and a second input connectable to receive a feedback value which is proportional to the current passed by the power transistor; wherein said filter amplifier and said error amplifier each comprise: a respective output transistor connected to drive said respective output, and a respective clamp circuit connected to limit the voltage of said output to a common constant voltage.
According to another disclosed class of innovative embodiments, there is provided: a control circuit, comprising: a filter amplifier comprising a first input operatively connected to receive a command voltage and a second input operatively connected to receive a reference voltage, and further comprising one or more passive elements connected therewith; an error amplifier, integrated with said filter amplifier, and comprising a first input operatively connected to be driven by an output of said filter amplifier, an output connectable to drive a power transistor, and a second input connectable to receive a feedback value which is proportional to the current passed by the power transistor; wherein said filter amplifier incorporates a clamp circuit, which is connected to limit the voltage of said output thereof to a predetermined constant voltage.
According to another disclosed class of innovative embodiments, there is provided: a control circuit, comprising: a power transistor, having a first current-carrying terminal thereof connectable to an inductive load and a second current-carrying terminal thereof operatively connected, through a sensing resistor, to a power supply voltage; a filter amplifier comprising a first input operatively connected to receive a command voltage and a second input operatively connected to receive a reference voltage, and further comprising one or more passive elements connected therewith; an error amplifier, integrated with said filter amplifier, and comprising a first input operatively connected to be driven by an output of said filter amplifier, an output operatively connected to drive a control terminal of said power transistor, and a second input connected to receive a voltage from said sensing resistor; wherein said filter amplifier and said error amplifier each comprise: a respective output transistor of a first majority-carrier conduction type connected to drive said respective output, and a respective clamp transistor of a second majority-carrier conduction type connected to limit the voltage on a control terminal of said respective output transistor, both said clamp transistors having respective control terminals thereof connected to a common constant voltage.
According to another disclosed class of innovative embodiments, there is provided: a motor control system, comprising: a power transistor, having a first current-carrying terminal thereof connectable to an inductive load and a second current-carrying terminal thereof operatively connected, through a sensing resistor, to a power supply voltage; a filter amplifier comprising a first input operatively connected to receive a command voltage and a second input operatively connected to receive a reference voltage, and further comprising one or more passive elements connected therewith; an error amplifier, integrated with said filter amplifier, and comprising a first input operatively connected to be driven by an output of said filter amplifier, an output operatively connected to drive a control terminal of said power transistor, and a second input connected to receive a voltage from said sensing resistor; wherein said filter amplifier and said error amplifier each comprise: a respective output transistor of a first majority-carrier conduction type connected to drive said respective output, and a respective clamp transistor of a second majority-carrier conduction type connected to limit the voltage on a control terminal of said respective output transistor, both said clamp transistors having respective control terminals thereof connected to a common constant voltage; and a DC motor in series with the power transistor.
According to another disclosed class of innovative embodiments, there is provided: a method of controlling a motor, comprising the substantially continuous and simultaneous steps of: generating a command signal indicating the difference between the actual speed of the motor and a desired speed of the motor; filtering said command signal, using a operational amplifier combined with at least one active component, to produce a compensated control voltage; controlling a power transistor, which is connected to drive the motor, by an error amplifier which is connected to receive said compensated control voltage and which is also connected to receive a feedback voltage indicative of the current passed by said power transistor; and controlling said error amplifier and said operational amplifier to clamp the respective outputs thereof in common.